1. Field of the Invention
The present invention relates to an exciter directly attached to a board for vibrating the board. In particular, the present invention relates to an exciter for directly vibrating a board which is designed so that when attached to a board via a bracket member, it will not be insufficiently fastened to the bracket member.
2. Description of the Related Art
In the past, in stereo systems, PCs, mobile phones, and other electronic apparatuses, speakers have been used to output audio information from various media. In such speakers, vibration boards for emitting sound are attached to exciters supplied with the drive signals for audio output. These vibration boards have horn shapes specially designed for such speakers. For example, the vibration boards have voice coils of exciters affixed to them. Sound is output by these voice coils vibrating by magnetic circuits.
Such speakers are also used to reproduce music or speech in vehicles, for example, the compartments of passenger cars. These speakers are for example built into the doors of the front seats or are placed on the rear trays. Usually a plurality of speakers are arranged attached to at least one of the front seat and rear seat sides.
In addition to arranging speakers for audio reproduction inside the front seat doors or on the rear trays, arrangement of speakers including direct drive exciters at the ceiling panels of the compartments has for example been disclosed in Japanese Utility Model Publication (Kokai) No. 6-45865. When attaching usual speakers in a compartment, there are restrictions on the positions of attachment of the speakers. Speakers of too large nominal sizes cannot be used. To deal with this, in the speakers proposed above, instead of the conventional speakers having large nominal sizes, exciters are directly attached to the ceiling panels and the ceiling panels are used as vibration boards.
Various exciters for directly vibrating boards able to be used for such car-mounted speakers have been proposed as disclosed for example in Japanese Unexamined Patent Publication (Kokai) No. 2003-143690. The proposed exciter for directly vibrating board is provided with a coupler member. It is for example directly fixed to a board such as an interior panel used for vehicles so as to thereby form speakers. If however the coupler member is fixed to the board, when for example the exciter is damaged and the speaker no longer function, it is not possible to replace only the exciter. That is, the entire board with the exciter attached has to be replaced.
Therefore, considering the servicing, just the exciter is made able to be replaced by fixing a bracket member to the board, attaching the exciter via the bracket member, and using the exciter to vibrate the board through the bracket member. That is, the exciter is attached to the board through the bracket member. This bracket member is shaped as a disk at the center of which a projection with male thread is provided. The coupler member is in turn provided at the center with recesses with female thread.
When the bracket member is for example fixed to the surfaces of the interior panel of vehicles, when attaching the exciter to the interior panel, the recesses formed at the coupler member and the projection of the bracket member is screwed together, that is, the exciter is turned to fasten it.
However, if workers manually turn exciters when attaching them, the fastening torques in the turning work cannot be made constant and sometimes sufficient fastening torques cannot be applied. The insufficient fastening at the time of attachment of the exciter causes loose attachment and degrades the performances of the speaker. Further, the exciters may even drop off.
To prevent insufficient fastening at the time of attachment of exciter, use of work tools such as wrenches able to easily give the required fastening torques may be considered. However, the only places for the ends of the work tools to be brought into contact with the exciter are the outer circumference of the outside yoke. The ends of the work tools end up slipping at the outer circumference, so sufficient fastening torques cannot be obtained.
On the other hand, if too strongly fastening the exciter—not only when attaching it, but also when detaching it for replacement, the ends of the work tools end up slipping at the outer circumference of the outside yoke and therefore the exciter cannot be turned.